INTEL ROBOTIC TABLET CHARGER

Portland State University

Maseeh College of Engineering & Computer Science

ME 493 Final Report – Year 2012

This report elaborates the final design details and evaluations showing that it meets the customer’s product design requirements.

Capstone

2012

Group Members:Garrett PauwelsJustin CareyHung NguyenKevin HughesNolan IgarashiRichard Mullenburg

Industry Sponsor:Dr. Douglas Heymann

Industry Advisor:Evan Waymire

PSU Advisor:Dr. David A. Turcic

June 11 2012

1 Executive Summary

The prototype and testing of the Intel Robotic Tablet Charger has been completed by the

Portland State University senior capstone team and is ready to be delivered and presented to

Intel. The team has gone through the final design process, manufacturing of the prototype and

completed evaluating that the customer’s product design specifications (PDS) were met. This

paperpresents the final chosen concept of the Robotic Tablet Charger, including testing and

evaluation results on various parts of the PDS document.

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2 Table of Contents

1 EXECUTIVE SUMMARY................................................................................................................................ 1

2 TABLE OF CONTENTS................................................................................................................................... 2

3 LIST OF FIGURES.......................................................................................................................................... 3

4 LIST OF TABLES........................................................................................................................................... 4

5 INTRODUCTION.......................................................................................................................................... 5

6 MISSION STATEMENT................................................................................................................................. 5

7 TOP-LEVEL ALTERNATIVE DESIGNS.............................................................................................................. 5

8 FINAL DESIGN............................................................................................................................................. 8

8.1 MECHANICAL DESIGN:......................................................................................................................................88.1.1 Chassis:...................................................................................................................................................88.1.2 Tablet Holder:.........................................................................................................................................88.1.3 Charging Station:....................................................................................................................................8

8.2 ELECTRICAL DESIGN:........................................................................................................................................9

9 DESIGN EVALUATION................................................................................................................................ 12

9.1 EVALUATION FOR SAFETY AND ERGONOMICS:.....................................................................................................129.2 EVALUATION FOR THE RELIABILITY:...................................................................................................................139.3 EVALUATION FOR MATERIAL AND MOBILITY:......................................................................................................139.4 EVALUATION FOR MAINTENANCE:....................................................................................................................139.5 EVALUATION FOR COST AND FINANCIAL PERFORMANCE:.......................................................................................149.6 EVALUATION OF STRUCTURAL INTEGRITY:...........................................................................................................14

10 CONCLUSION............................................................................................................................................ 15

11 REFERENCES.............................................................................................................................................. 16

12 APPENDIX A.............................................................................................................................................. 17

12.1 DESIGN EVALUATION:....................................................................................................................................1712.2 PRODUCT DESIGN SPECIFICATION DETAILS:........................................................................................................17

13 APPENDIX B.............................................................................................................................................. 20

13.1 MOTOR SIZING EQUATIONS.............................................................................................................................2013.2 CHASSIS SIZING ANALYSIS................................................................................................................................22

14 APPENDIX C.............................................................................................................................................. 25

14.1 PROJECT GANTT CHART..................................................................................................................................25

15 APPENDIX D.............................................................................................................................................. 26

15.1 DETAILED DRAWINGS:....................................................................................................................................26

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15.1.1 Charging Station..............................................................................................................................2615.1.2 Charging Station: Female.................................................................................................................3215.1.3 Charging Station: Male....................................................................................................................37

15.2 ROBOT:.......................................................................................................................................................4215.2.1 2Amp Fuse........................................................................................................................................4215.2.2 Battery Block....................................................................................................................................4315.2.3 Ball Caster........................................................................................................................................4415.2.4 Chassis.............................................................................................................................................4515.2.5 H-bridge...........................................................................................................................................5015.2.6 Switch...............................................................................................................................................5115.2.7 Wheel Hub.......................................................................................................................................5215.2.8 Tablet Holder...................................................................................................................................53

16 APPENDIX E.............................................................................................................................................. 59

16.1 BILL OF MATERIALS.......................................................................................................................................59

3 List of Figures

FIGURE 1. TABLET CHARGING STATION AND ENTIRE ROBOT ASSEMBLY PRIOR TO ENGAGEMENT......................................................10FIGURE 2.TABLET CHARGING STATION AT ENGAGEMENT SHOWING MALE-COVER LIFTED AND CONNECTION BETWEEN RODS AND POINTS.

..........................................................................................................................................................................10FIGURE 3. ELECTRICAL COMPONENTS OF THE INTEL ROBOT TABLET CHARGER AND THEIR LOCATIONS.............................................11FIGURE 4.DETAILED ELECTRICAL SCHEMATIC.A EZ-BOARD V3 IS THE CONTROL BOARD, ALONG WITH THE 'RED' H-BRIDGE.................11FIGURE 5: FREE BODY DIAGRAM OF A DRIVE WHEEL INDICATING A DRIVING TORQUE AT THE CENTERLINE, WITH FRICTION PRESENT.......20FIGURE 6: A LOAD OF 3 LBS IS APPLIED TO THE TOP OF THE ROBOT, COMPARE THREE DIFFERENT SHEET METAL SIZES TO DETERMINE THE

BEST OPTION FOR THE APPLICATION...........................................................................................................................22FIGURE 7: APPLIED PRESSURE LOAD OF .122 LB/SQR IN AND NECESSARY BOUNDARY CONDITIONS TO FULLY CONSTRAIN THE STRUCTURE.

..........................................................................................................................................................................23FIGURE 8. PROJECT GANTT CHART SHOWING TIMELINE AND COMPLETION DATES OF PROJECT.......................................................25FIGURE 9. CHARGING STATION: BASE- LEFT.........................................................................................................................26FIGURE 10. CHARGING STATION: BASE- RIGHT.....................................................................................................................27FIGURE 11.CHARGING STATION: BASE- SUPPORT.................................................................................................................28FIGURE 12.CHARGING STATION: FEMALE- BASE...................................................................................................................29FIGURE 13.CHARGING STATION: LEFT GUIDE.......................................................................................................................30FIGURE 14.CHARGING STATION: RIGHT GUIDE.....................................................................................................................31FIGURE 15.CHARGING STATION: FEMALE- BACK PLATE..........................................................................................................32FIGURE 16.CHARGING STATION: FEMALE- CONTACT.............................................................................................................33FIGURE 17.CHARGING STATION: FEMALE- PIN....................................................................................................................34FIGURE 18.CHARGING STATION: FEMALE- POINT..................................................................................................................35FIGURE 19.CHARGING STATION: FEMALE- SUPPORT..............................................................................................................36FIGURE 20.CHARGING STATION: MALE- BRACKET.................................................................................................................37FIGURE 21.CHARGING STATION: MALE- COVER PIN..............................................................................................................38FIGURE 22.CHARGING STATION: MALE- COVER....................................................................................................................39FIGURE 23.CHARGING STATION: MALE- PIN........................................................................................................................40

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FIGURE 24.CHARGING STATION: MALE- SUPPORT................................................................................................................41FIGURE 25. ROBOT: FUSE BASE.........................................................................................................................................42FIGURE 26.ROBOT: BATTERY BLOCK...................................................................................................................................43FIGURE 27.ROBOT: BALL CASTER.......................................................................................................................................44FIGURE 28.ROBOT: CHASSIS- BOTTOM FRAME.....................................................................................................................45FIGURE 29.ROBOT: CHASSIS- MOTOR BLOCK.......................................................................................................................46FIGURE 30.ROBOT: CHASSIS- REAR BRACKET.......................................................................................................................47FIGURE 31.ROBOT: CHASSIS- TABLET BRACKET.....................................................................................................................48FIGURE 32.ROBOT: CHASSIS- TOP FRAME...........................................................................................................................49FIGURE 33.ROBOT: H-BRIDGE BLOCK.................................................................................................................................50FIGURE 34.ROBOT: SWITCH SUPPORT................................................................................................................................51FIGURE 35.ROBOT: WHEEL HUB.......................................................................................................................................52FIGURE 36.ROBOT: TABLET HOLDER- BOTTOM SPACER..........................................................................................................53FIGURE 37. ROBOT: TABLET HOLDER- CHARGER BASE............................................................................................................54FIGURE 38. ROBOT: TABLET HOLDER- LEFT GUIDE.................................................................................................................55FIGURE 39. ROBOT: TABLET HOLDER- RIGHT GUIDE..............................................................................................................56FIGURE 40. ROBOT: TABLET HOLDER- TABLET SLIDE..............................................................................................................57FIGURE 41. ROBOT: TABLET HOLDER- TABLET SPACER...........................................................................................................58

4 List of Tables

TABLE 1. COMPARISON BETWEEN THREE CHASSIS AND TWO TABLET HOLDER DESIGNS HIGHLIGHTING THEIR BENEFITS AND ISSUES..........6TABLE 2.EVALUATION PROCESS OF THE FUNCTIONALITY AND PERFORMANCE OF THE ROBOT..........................................................12TABLE 3.EVALUATION PROCESS OF THE SAFETY AND ERGONOMICS OF THE ROBOT.......................................................................13TABLE 4.CONCEPT DESIGN EVALUATION MATRIX OF THE CHOSEN DESIGNS AND THEIR WEIGHTED TOTALS........................................17TABLE 5. SAFETY CRITERIA...............................................................................................................................................17TABLE 6. ERGONOMIC CRITERIA........................................................................................................................................17TABLE 7. PERFORMANCE CRITERIA.....................................................................................................................................17TABLE 8. ENVIRONMENTAL CRITERIA..................................................................................................................................18TABLE 9. COMPANY CONSTRAINTS CRITERIA........................................................................................................................18TABLE 10. TESTING & DOCUMENTATION CRITERIA...............................................................................................................18TABLE 11. MAINTENANCE CRITERIA...................................................................................................................................18TABLE 12. SIZE & SHAPE CRITERIA....................................................................................................................................18TABLE 13. AESTHETICS CRITERIA.......................................................................................................................................18TABLE 14. MATERIALS CRITERIA........................................................................................................................................19TABLE 15: OBTAINED F.E.A RESULTS FOR THE THREE METAL SIZES...........................................................................................24TABLE 16. BILL OF MATERIALS..........................................................................................................................................59

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5 Introduction

Tablets provide a means of escape and entertainment. Immobile individuals who use tablets must

have a source for charging their tablet. Often, the locations of wall outlets are not always

accessible for these individuals. The current market does not provide a means for transporting a

tablet in need of charging to a designated charging station. Furthermore, current market tablet

chargers plug into standard 60Hz wall outlets or computer universal serial bus (USB) ports. The

locations of these are not ergonomically designed for individuals with limited mobility and

reach. Because of this, injury could be a result of over exertion.

6 Mission Statement

The goal of our team is to design and prototype a robotic device which will transport a tablet in

need of being energized to a designated charging station. This will resolve any issues of charging

the tablet and ergonomics of the current charging methods for persons of limited mobility. The

Robot Tablet Charger prototype will abide by all PDS requirements and be presented at the Intel

Hillsboro Campus in June 2012.

7 Top-Level Alternative Designs

In the research and development stages for the basic structure of the robot, a number of ideas

were evaluated and discussed. These designs were compared to a set of requirements established

by the PDS report. A list of the requirements and their summaries that the robot must satisfy is

presented below.

Maneuverability: depends on how well the design is capable of a turning 180 degrees

Weight: depends on the number of components as well as the materials used

Stability: the number of wheels and placement of the wheels

Cost: based on number of components and materials

Simplicity: based on design and selected components

Ease of Use: depends on location and design

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From this list a total of three robot chassis; two tablet holders and two charging station designs

were developed. The benefits and issues of each design are represented below in Table 1.

Table 1. Comparison between three chassis and two tablet holder designs highlighting their benefits and issues.

Design Benefits Issues Figure

Chassis – A

Stable Less material

required Lightweight Tighter turning

radius

Additional parts required

Chassis – B

Stable Tight turning

radius

Difficult to manufacture

Too many parts Solid axle

produces turning issues

Chassis – C

Tight turning radius

Light weight Fewer parts

required

Unstable Higher

manufacturing cost

Holder – A

Easy to manufacture

No movingcomponents

Strong one- piece design

Weight Lack of

adjustability Hard to

manufacture

Holder –B

Cheaper to manufacture

Less time to manufacture

Less material needed

Lightweight

More parts are required to construct

Not as rigid

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Charger – A

Less material required.

Less resistance with connection

More rigid

Complex design More time

required to manufacture

Sharp edges

Charger – B Simplistic design Self-centering

platform

Needs precious alignment

Less rigid More parts

required

From the scoring matrix presented in Appendix A and Table 1, it was concluded that tablet

holder B, charging station A and chassis A were the most beneficial design. The major reasons

for choosing chassis A is due to its maneuverability and stability. This is generated by the two

drive wheels and the two ball casters. The casters provide the robot with a tighter turn radius and

the capability to avoid objects. Also they give the robot a lower center of gravity and the proper

ground clearance.

The major reasons for choosing the tablet holder design B is its adjustability and less material is

required for manufacturing. The major issues with design A of the tablet holder is that it would

require a lot more time to produce. Furthermore, it doesn’t conform to the constraints of the rapid

prototype machine.

The major reasons for going with the charging station design A is that the contacts require less

force to make a connection. The issues that developedwith charging station design A is that the

platform doesn’t provide an adequate self-centering unit and more moving parts are required to

make a connection. These moving parts can lead to error in the connection process if the

components are not held to a tight tolerance in the construction phase.

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8 Final Design

The team came to an agreement that the choices of chassis A, tablet holder B and charging

station design A will fulfill all the major requirements established in the PDS. These

requirements consist of having the capability of traveling over multiple surfaces, having a low

center of gravity and providing an easy interface with the included tablet. The design will consist

of two motorized driving wheels and two metal ball casters for stability in the front and rear of

the robot. This design will best fit our requirements due to a decrease in turning radius. To keep

the center of gravity low, the batteries, control board and two electric motors will be mounted on

internal brackets that are suspended 1.5 inches off the ground. This ground clearance will be

sufficient for traveling over carpets and other low obstructions.

8.1 Mechanical Design:

8.1.1 Chassis:In parallel to designing a chassis for the Robot Tablet Charger, FEA analysis was performed on

several different thicknesses of sheet metal.We used this information to size the correct gauge of

material to avoid deformation [see Appendix B]. For the purpose of cost, strength and the ease to

modify the design— chassis A was sent off to Eagle Precision to be manufactured using 18

gauge low carbon steel. With the precision needed for the holes in the chassis to mount the

electrical parts, Eagle Precision was required to drill the holes. The chassis was then assembled

using 3mm bolts with washers and self-locking nuts. A completely assembled chassis can be

seen in Figure 1.

8.1.2 Tablet Holder:A non-metal tablet holder was chosen because the team wanted to utilize Intel’s 3D printer due

to the low cost and short lead time. Intel’s 3D printer could accommodate parts that fit within a

10”x10”x10” space. Thus,due to the space limitations of Intel’s 3D printer, our group

manufactured the assembly in many parts that were then later assembled. After the holder was

assembled and mounted to the chassis using 3mm bolts; the team decided that having a single

steel L-bracket did not make the holder rigid enough. Therefore, two L-brackets were utilized.

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8.1.3 Charging Station:The charging station was designed to allow the robot to interface the tablet and battery with a

wall charger with ease. The overall charging station design was constructed out of ABS

Polycarbonate plastic by Intel’s 3D printer and 3mm bolts were used to assemble. The main

assembly consists of the platform, cross member supports and guides. The guide’s purpose is to

self-align the robot prior to engagement for charging. The charging station (seen in figures 1 and

2) also consists of a male and female assembly, each of which must come into contact to

complete the electrical connection.

Female

The female charging assembly consists of a back plate, female support and brass points; all of

which were assembled using 3mm bolts. The main achievement in the design of this assembly is

to protect the connection points for safety reasons and to allow the male cover to lift in order to

complete the connection. The male brass pins come into contact with the female brass points

creating the connection. However, to make sure a connection is always achieved, the points act

as a spring to guarantee a good connection. This can be seen in Figure 2.

Male

The male charging assembly consists of a base, support, cover and brass rods; all of which were

assembled using 3mm bolts. The cover in this assembly protects the brass rods for safety until

making contact with the female support, lifting the cover open exposing the rods. There are a

total of four rods, two of which are positive and negative. One set of rods are used for charging

the tablet, and the other set are used for charging the robot battery pack. This can be seen in

Figure 2.

8.2 Electrical Design:

The main electrical components for the final design comprised of two motors, a control board

and H-Bridge, a two amp fuse, a single rechargeable battery pack, an on/off switch and

miscellaneous connectors. A detailed layout of these parts and electrical schematic can be seen in

Figure 3 and 4. The major achievement that our group had was in controlling the motors and

being able to wireless control the robot. The software that was used is provided by EZ-Robot and

was very simple to operate.

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Figure 1. Tablet charging station and entire robot assembly prior to engagement.

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Figure 2.Tablet charging station at engagement showing male-cover lifted and connection between rods and points.

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Figure 3. Electrical components of the Intel Robot Tablet Charger and their locations

Figure 4.Detailed electrical schematic.A EZ-Board V3 is the control board, along with the 'red' H-Bridge

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9 Design Evaluation

The crucial components that the robot must fulfill for the performance and functionality of the

customer needs is as follows; ability to recharge the battery of the robot and tablet once docked;

be capable of rotating 180 degrees; have a wireless proximity of forty feet and be able to travel

over multiple surfaces. The method that will be utilized to evaluate the ability to recharge the

tablet and robot is to dock the chassis into the charging station and test the amount of voltage

emitted from the connections. If the voltage output of the connections is equal to the input

voltage then it can be concluded that there is no voltage drop in the circuit. The testing

procedures of the maneuverability of the robot will involve having it rotate 180 degrees in one

spot for three consecutive trials. The proximity and multi-surface test will be done

simultaneously by having the robot travel forty feet over tile, rug, and hardwood surfaces.

Furthermore, the control board and motors of the robot were powered by a 7.2V rechargeable

battery and therefore meets the criteria of under 14V Power Source. The evaluation for the

function and performance is shown in Table 2 below.

Table 2.Evaluation process of the functionality and performance of the robot.

Requirements Actual Goal MetAbility to recharge tablet: 19.0 volts 19V YesBattery voltage < 14V 7.2V YesRotation angel: 180 degree 360 degree YesDistance travel: 40 feet 52 feet YesTravel over hardwood - YesTravel over carpet - YesTravel over tile - Yes

9.1 Evaluation for Safety and Ergonomics:

The chassis of the robot is designed to eliminate most electrical hazards. The body of the robot is

covered by metal sheets which have the circuit put completely inside. All wire connections are

covered by heat shrink to avoid being touched by mistake. The brass rods (seen in Figure 2) on

the robot are designed to have a cover that will then lift exposing the rods when the robot docks.

When the tablet is in position for recharging, the total height of the system is 16 inches (See

Table 3). This is high enough for the users to eliminate any abnormal bending motion while

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sliding the tablet into the tablet holder. Therefore it can help the users avoid injury when using

the robot.

Table 3.Evaluation process of the safety and ergonomics of the robot.

Requirements Actual Goal MetHeight > 6.0 inch 16 inch YesAvoid injury - YesAvoid Electrical hazards - Yes

9.2 Evaluation for the Reliability:

The life span of the battery as well as all electrical devices can be decreased if the connections

are interrupted. Therefore, the surface of the docking station has stops designed to keep the robot

stable in charging position, which helps the system being connected to the outlet continuously.

The mission of the Robotic Tablet Charger is not only charging the tablet but the battery for the

robot itself. To help users not be confused between the plug for the battery and the tablet, one is

designed to be a male plug and the other is female.

9.3 Evaluation for Material and Mobility:

Although this robot is a mobile device, it needs to have an appropriate size that can be noticed

easily to avoid accidents. The prototype of the Intel Robotic Charger has the dimension of

9x9x11inch (LxWxH), which can be observed clearly when people are walking in the room. The

total weight of the robot is 5.0lb, It is heavy enough to not being tiped up when the tablet is

secured in the tablet holder. The sheet metal body is hard enough to support all the robot and the

tablet without being deformed when the robot moves (see Appendix B).

9.4 Evaluation for Maintenance:

If maintenance is required, access to the inside of the robot chassis requires the removal of 8

easily accessible screws. The tools required to remove the top of the chassis are an 8mm

crescent wrench, a Philips head screwdriver and a 5mm Allen wrench. Access to replaceable

parts, such as the fuse, are easily accessible without the removal of chassis components.

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9.5 Evaluation for Cost and Financial Performance:

The overall cost of the Robotic Tablet Charger is $234.56 out of a $500.00 budget set by our

sponsor. We came very much so under budget due to the ability to use Intel's 3D printer and

Eagle Precision for the sheet metal parts. A complete Bill of Materials can be seen in Appendix

E.

9.6 Evaluation of Structural Integrity:

Severe deformation of the sheet metal due to the loading caused by tablet transport cannot be

tolerated. An adequately stiff frame was determined through use of Finite Element Analysis to

choose 18 gauge steel as the building block for the chassis (see Appendix B).

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10 Conclusion

In conclusion, the robotic tablet charging system designed by this capstone team fulfills all major

requirements set forth by the customer in the PDS requirements, all while remaining within

budget. The final design of the robotic charger is able travel more than 40 ft wirelessly, turn 360

degrees, operate on multiple surfaces, and successfully transport the tablet for charging. The

docking station works as designed and is able to help correctly align the charging contacts, of

both the robot and tablet, even if its approach is not exactly head-on. Currently the robotic

charger needs to be controlled manually with a Bluetooth enabled device both to pick up the

tablet and to return to the docking station. The team is working on a method of automating the

robot so that it will be able to return to its docking station autonomously after being controlled to

the tablet’s location. In addition, a shell is to be designed to place over the chassis to give the

robot a more finished look.

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11 References

1. Engineers Edge, Sheet Metal Gauge Sizes Data. Accessed: June 03 2012.

<http://www.engineersedge.com/gauge.htm>/

2. MatWeb, Material Property Data. AK Steel ASTM A 570, Grade 30 Hot Rolled Carbon

Steel, Structural Quality. Accessed: June 03 2012.

<http://matweb.com/search/DataSheet.aspx?

MatGUID=24a971583d324d1da526bdc4001193dd>

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12 Appendix A.

12.1 Design Evaluation:

Table 4.Concept design evaluation matrix of the chosen designs and their weighted totals.

Maneuverability Weight Stability Cost Simplicity Ease of Use Weighted TotalChassis Designs

Chassis A 4 3 3 3 4 - 11Chassis B 3 3 3 3 3 - 9Chassis C 2 4 5 4 2 - 9

Tablet HolderHolder A - 3 - 4 2 3 4Holder B - 2 - 2 5 4 10

12.2 Product Design Specification Details:

Listed below is the Product Design Specifications developed from the information provided by

Intel. The design criteria contained in the tables has been prioritized to fit the customer needs.

Table 5. Safety Criteria

Safety

Criteria Customer Metric Target Basis Verification Priorit

y

Electrical shockIntel

Design &material

Aluminum &

plastic

Electrical hazardstandards

Electrical measuringequipment High

User & robotcollision

Vision distance(in) 24 Avoid collision Experiment

Table 6. Ergonomic Criteria

ErgonomicCriteria Custome

r Metric Target Basis Verification Priority

Convenientoperation Intel Height (in) > 6.0 Avoid injury Measurement High

Table 7. Performance Criteria

Performance

Criteria Customer Metric Target Basis Verification Priority

Battery powered

Intel

Battery pack 1 Supplied batteryharness Motors operational

HighRechargeablebattery Volts

< 12.0 Controller capacity Plug into outlet

Utilize outlet charging station 110 Wall outlet Robot placed on

charging station

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Table 8. Environmental Criteria

Environment

Criteria Customer Metric Target Basis Verification Priority

Travel overhardwood

Intel Inch

0 Flat and smooth Robot tested onhardwood

HighTravel over carpet 1 Different surface

heightsRobot tested on

carpetTravel over tile 0 Different textures Robot tested on tile

Table 9. Company Constraints Criteria

CompanyConstraint

s

Criteria Customer Metric Target Basis Verification Priority

Compatibility with

CL900 tabletIntel 2.1mm barrel

power jack Yes Tablet to interfaceand charge Manufacturing High

Table 10. Testing & Documentation Criteria

Testing

Criteria Customer Metric Target Basis Verification Priority

Testing the design

Intel

Number of tests < 10.0 To refine the

designFull test run w/o

any issues

HighRobots ability tointerface with

charging station

Inches off fromideal position 1

Robot may not enter

charging stationcorrectly

Test robot enteringcharging station

Table 11. Maintenance Criteria

Maintenance

Criteria Customer Metric Target Basis Verification Priority

Use common toolsUser/Intel

# of tools required < 3.0 Component

replacementprocess

Design stages MediumAccessiblecomponents

# of componentsto maintain 3

Table 12. Size & Shape Criteria

Size & Shape

Criteria Customer Metric Target Basis Verification Priority

Ground Clearance

Intel Inch

1.5Accommodatefor all ground

surfacesDesign stages LowRobot width 12 Stability/

accommodatefor components

Robot length 12Height of robot 16

Table 13. Aesthetics Criteria

Aesthetics

Criteria Customer Metric Target Basis Verification Priority

Attractive General public Yes/No

Should be visually

appealing

design attracts attention Provide a survey Low

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Table 14. Materials Criteria

Materials

Criteria Customer Metric Target Basis Verification Priority

Light weightUser/Intel

lbs < 10.0If batteries die, one

must manuallymove robot

Weigh / designanalysis Low

Semi-disposable % Recyclable > 75.0 Environmentallyresponsible Design

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13 Appendix B.

13.1 Motor Sizing EquationsObjective:

The purpose of the following calculations are to determine adequate motor torque to move our

robot. It is important to select a motor that has enough torque, but does not sacrifice linear

velocity. The PDS requirement that involves the robot traveling over forty feet pertains to this

limitation; if the speed is too slow, the robot will take a very long time to navigate.

It was found that a motor torque of approximately 115 oz*in would be sufficient to break static

friction between the rubber wheels and concrete, causing the robot to slip as it traversed its

course. We believe appropriate assumptions were applied in order to come to this conclusion

with a factor of safety (FOS) = 2 applied to the weight of the robot.

Given:

A drive wheel with a torque applied at the wheels center line is at rest on a hard surface such as

wood or concrete. Find the torque necessary to break contact between the two surfaces.

Figure 5: Free body diagram of a drive wheel indicating a driving torque at the centerline, with friction present.

The purpose of this analysis is to find the torque that will break the static frictional force.

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Assumptions:

Weight of the total robot is roughly 12 pounds and is supported by the two drive

wheels, W = 12lbfFOS = 2

Static friction coefficient is between concrete and rubber, μs= .8

Wheel diameter is 3 inches, D = 3in

Solution:

Summing the forces in the Y direction yields,

ΣFy=0⇒N−W2

=0

N=W2

=6 lbf

Summing moments about the shaft centerline,

ΣMo=0⇒ Ff∗D2

−T 1=0

Substituting for the frictional force Ff = μsN,

T 1=μsND2

T 1=0.8∗6lb∗3∈¿2¿

T 1=7.2lb∗¿=115 oz∗i n

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13.2 Chassis sizing analysis Objective:

The purpose of performing an analysis on the chassis is to determine an adequate structure for

transporting the tablet. The greatest force on the system would be when the robot is stationary

and the user loads the tablet into the tablet holder and presses it into the barrel jack. It is,

therefore, necessary to implement a static analysis for the entire structure. Without proper

support, the robot will not meet the PDS requirement of traveling over 40 feet.

The following analysis is comprised of a Finite Element Analysis. Three different sheet metal

sizes- 18, 20, and 22 gauge- have been chosen for analysis to compare against one another. It

was determined that 18 gauge sheet metal was an adequate material for chassis construction.

Because the final chassis design is not chosen, analysis is based on a preliminary design. It is

believed that an adequate FOS of 4 has been applied to the load on the top sheet to account for

excessive force during the docking process.

Given:

A load of 3 pounds is applied to the top surface of the structure shown in fig 6. Three low carbon

steel sheet metal sizes – 18, 20, and 22 AWG- are to be analyzed to determine the best option.

Figure 6: A load of 3 lbs is applied to the top of the robot, compare three different sheet metal sizes to

determine the best option for the application.

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Assumptions:

A FOS of 4 is applied to the load the tablet causes to account for uncertainties in loading characteristics, F = 12 lbs

The load is evenly distributed across the top of the chassis, P=FA

= 12lb70.8¿2 =.122 lb

¿2

18 AWG steel thickness = 0.048 in [1] 20 AWG steel thickness = 0.036 in [1] 22 AWG steel thickness = 0.030 in [1] The chassis is constrained at the motor wheel connection as well as the caster

location.

Solution:

Because the chassis is symmetric in one direction, the analysis can be split in half. A symmetry

constraint replaces the previously present material. Two fixed constraints are applied to simulate

bolting on the structure, see Fig 6. It is assumed that the two plates cannot move relative two

each other in the highlighted areas due to the clamping force applied by the bolts. A static, linear

analysis was implemented for each metal size with the results shown in Figure 7. The stress and

displacement values are listed in Table 15 to summarize the findings.

Figure 7: Applied pressure load of .122 lb/sqr in and necessary boundary conditions to fully constrain the

structure.

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Fixed constraint

Fixed constraint

Figure 7B: Shown from left to right are the displacement magnitude results for 18,20,22 AWG sheet metal sizes.

Table 15: Obtained F.E.A results for the three metal sizes

Metal Size (AWG)

Max Stress (ksi)

Max Displacement (in)

18 1.38 0.01320 2.45 0.03122 3.45 0.054

As Shown in Table 15, all sheet metal sizes, theoretically, are adequate for supporting the load;

the Yield stress for low carbon steel is approximately 30 ksi. [2]

Since yielding is of no concern in all three cases, it is necessary to compare displacement. Our

robot will have very little clearance between the motors and the top plate. Also, charging

connection components will be attached in the center of the robot with little clearance as well.

For this reason, little deflection is desired; 18 gauge steel has the least amount of deflection and

is therefore chosen for our application.

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Max displacement and Stress

14 Appendix C.

14.1 Project Gantt Chart

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Figure 8. Project Gantt chart showing timeline and completion dates of project

15 Appendix D.

15.1 Detailed Drawings:

15.1.1 Charging Station

Figure 9. Charging Station: Base- left

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Figure 10. Charging Station: Base- right

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Figure 11.Charging Station: Base- support

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Figure 12.Charging Station: Female- base

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Figure 13.Charging Station: Left guide

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Figure 14.Charging Station: Right guide

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15.1.2 Charging Station: Female

Figure 15.Charging Station: Female- back plate

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Figure 16.Charging Station: Female- contact

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Figure 17.Charging Station: Female- pin

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Figure 18.Charging Station: Female- point

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Figure 19.Charging Station: Female- support

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15.1.3 Charging Station: Male

Figure 20.Charging Station: Male- bracket

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Figure 21.Charging Station: Male- cover pin

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Figure 22.Charging Station: Male- cover

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Figure 23.Charging Station: Male- pin

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Figure 24.Charging Station: Male- support

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15.2 Robot:

15.2.1 2Amp Fuse

Figure 25. Robot: Fuse base

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15.2.2 Battery Block

Figure 26.Robot: Battery block

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15.2.3 Ball Caster

Figure 27.Robot: Ball caster

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15.2.4 Chassis

Figure 28.Robot: Chassis- bottom frame

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Figure 29.Robot: Chassis- motor block

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Figure 30.Robot: Chassis- rear bracket

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Figure 31.Robot: Chassis- tablet bracket

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Figure 32.Robot: Chassis- top frame

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15.2.5 H-bridge

Figure 33.Robot: H-bridge block

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15.2.6 Switch

Figure 34.Robot: Switch support

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15.2.7 Wheel Hub

Figure 35.Robot: Wheel hub

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15.2.8 Tablet Holder

Figure 36.Robot: Tablet holder- bottom spacer

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Figure 37. Robot: Tablet holder- charger base

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Figure 38. Robot: Tablet holder- left guide

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Figure 39. Robot: Tablet holder- right guide

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Figure 40. Robot: Tablet holder- tablet slide

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Figure 41. Robot: Tablet holder- tablet spacer

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16 Appendix E.

16.1 Bill of Materials

Table 16. Bill of Materials

Item Part number Description Manufacturer

Cost (not incl

S&H)Unit Quan

tity

Total Unit Cost

1 6468002 TENERGY 7.2V RC Car Battery

Fry's Electronics $24.99 EA 1 $24.99

2 1445 67:1, 6mm shaft, Metal Gear motor Pololu $39.95 EA 2 $79.90

3 1439 Pololu Wheel 90x10mm Pair - Black Pololu $9.95 PK 1 $9.95

4 713 TB6612FNG Dual Motor Driver Pololu $8.45 EA 1 $8.45

5 2184 Servo Extension Cable 12" Male - Female Pololu $2.49 EA 6 $14.94

6 5864493 FUSE BLOCK Fry's Electronics $1.79 EA 1 $1.79

7 GMA_5x_2A

GMA 2A 250v Fast Blow Fuses Amazon $3.99 PK 1 $3.99

8 1945892 SLIDE SWITCH DPDT ON/ON

Fry's Electronics $0.99 EA 2 $1.98

9 955 Ball Caster with 3/4" Metal Ball Pololu $4.99 EA 1 $4.99

10 B001RNFQK8 Male 2.1mm Plug Pigtail Amazon $9.99 EA 1 $9.99

11 B001RNHQ3S

Female 2.1mm Plug Pigtail Amazon $5.49 EA 1 $5.49

12 95947A010

Metric Aluminum Female Threaded Hex Standoff

4.5mm Hex, 14mm Length, M3 Screw Size

McMASTER-CARR $0.68 EA 4 $2.72

13 92005A118

Metric Pan Head Phillips Machine Screw Zinc-Plated Steel, M3 Size,

8mm Length, .5mm Pitch

McMASTER-CARR $2.60

PK/100P

C1 $2.60

14 91166A210

DIN 125 Zinc-Plated Class 4 Steel Flat Washer M3 Screw Size, 7mm OD,

.45mm-.55mm Thick

McMASTER-CARR $1.55

PK/100P

C1 $1.55

15 93245A098

Metric Alloy Steel Flat Point Sckt Set Screw M3 Size, 4mm Length, .5mm

Pitch

McMASTER-CARR $8.19

PK/100P

C1 $8.19

16 90576A102

Metric Zinc-Plated Steel Nylon-Insert Locknut

Class 8, M3 Screw Size, .5mm Pitch, 5.5mm

W, 4mm H

McMASTER-CARR $3.09

PK/100P

C1 $3.09

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17 None Wheel hubs PSU MachineShop $0.00 EA 2 $0.00

18 None 3D printer parts Intel $0.00 EA 25 $0.00

19 None Sheet metal parts Eagle Precision $0.00 EA 2 $0.00

20 702 IR Sensor Pololu $49.95 EA 1 $49.95TOTAL

: $234.56

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